Biological explanations for Schizophrenia - The Dopamine Hypothesis

Dopamine

  • Chemical substance (neurotransmitter) manufactured in brain that transmits messages between neurones

  • Appears to work differently in patients with schizophrenia

  • Particularly important in the functioning of several brain systems that may cause symptoms of schizophrenia - in particular, the cortex and sub-cortex

  • In a nutshell…

    • Schizophrenia is caused by high levels of dopamine

    • Schizophrenics either produce too much dopamine or have too many dopamine receiving neurones

    • This results in dopamine firing too often, which is turn results in a distortion in attention and perception, which causes hallucinations

  • However, a more recent version of the dopamine hypothesis states the following:

    • Schizophrenia can also be linked to low levels of dopamine

    • Low dopamine levels are linked to disordered thinking

Hyperdopaminergia: Excessive levels of dopamine in the sub-cortex and Broca’s area

Hypodopinergia: Low levels of dopamine in the prefrontal cortex

Other neural correlates

  • Neural correlations: patters of structure or activity in the brain that occur with a schizophrenic experience. As they occur simultaneously this could lead us to believe that the patterns observed are implicated in causing schizophrenia

  • Avolition which involves motivation, has been associated with one of the main reward centres in the brain. The Ventral Striatum is crucial in the anticipation of reward.

    • Juckel et al (2006) measured activity levels here and found lower levels of activity in schizophrenics compared to controls.

  • Negative correlation between activity levels and severity of avolition. As activity levels increase, avolition decreases. As activity decreases, avolition increases. Vental striate is a neural correlate of negative symptoms.

  • Positive symptoms also have neural correlates.

    • Allen et al (2007) scanned patients with auditory hallucinations, compared to a control. Lower activation levels were found in superior temporal gyrus and anterior cingulate gyrus of hallucinations group. Reduced activity in these parts of the brain is a neural correlate for auditory hallucinations.